Tungsten-nickel-iron-molybdenum die casting shaping members

ABSTRACT

This invention is directed to the use of tungsten base alloys containing about 1 to 12 weight percent nickel, about 0.5 to 8 weight percent iron and about 0.5 to about 8 percent molybdenum for die casting dies, molds, cores and other metal shaping members.

United States Larsen Patent [15] 3,656,731 1 Apr. 18, 1972 [54] TUNGSTEN-NICKEL-IRON- MOLYBDENUM DIE CASTING SHAPING MEMBERS Earl I. Larsen, 9565 Copley Drive, Indianapolis, 1nd. 46260 Inventor:

Filed: Sept. 5, 1969 App1.No.: 855,701

Related 0.8. Application Data References Cited UNITED STATES PATENTS Milligan et a1. 148/133 FOREIGN PATENTS OR APPLICATIONS 204,184 1 H1956 Australia ..75/176 1,137,064 5/1957 France ..75/176 OTHER PUBLICATIONS Precision Metal Molding, October 1965, pp. 37 & 38 TS200.P74

Precision Metal Molding, February 1966, Vol. 24, No. 2, page 32, TS200.P74

Primary Examiner-R. Spencer Annear Attorney-Richard H. Childress, Robert F. Meyer, Henry W. Cummings and C. Carter Ells, Jr.

[5 7] ABSTRACT This invention is directed to the use of tungsten base alloys containing about 1 to 12 weight percent nickel, about 0.5 to 8 weight percent iron and about 0.5 to about 8 percent molybdenum for die casting dies, molds, cores and other metal shaping members.

18% Ni9%CO-5% MO- .6% Ti -O.l% Al BALANCE F 95% w-4% Ni 2% Fe-4%M0A SURFACE ROUGHNESS (INCHES X 10 8 12 CYCLES X 1000 l6 4 ms PATENTEDAPR 18 m2 3. 656 7531 saw 2 BF 2 Z INVENTOR EARL I. LARSEN W ATTORNEY TIJNGSTEN-NICKEL-IRON-MOLYBDENUM DIE CASTING SHAPING MEMBERS This application is a continuation-in-part of application Ser. No. 645,041, filed June 9, I967, now abandoned, which in turn is a continuation-in-part of application Ser. No. 590,088 filed Oct. 27, 1966 now abandoned.

Prior to this invention, most of the materials used as die casting dies, molds, cores, core pins and other metal shaping members were made from tool steel. A typical tool composition for such die casting molds contains about 5 percent chromium, 0.4 percent carbon and minor amounts of vanadium and molybdenum.

While such tool steel dies are fairly satisfactory for forming low melting point metals and alloys of zinc, magnesium, and

aluminum, a die material that would have longer life, resist erosion better, resist spalling and cracking, and be easier to .machine would be highly desirable. When die casting the l,000 castings have been made. Such spalling and cracking occurs when the die is subjected to thennal stresses created by the molten high temperature alloys being forced into the die under high pressure; while erosion of the die is generally caused by the washing action of such high temperature alloys.

It is, therefore, an object of the invention to provide a die casting dies or molds, cores and other metal shaping members which have a long life.

It is another object of the invention to provide a die casting dies, molds, cores, core pins and other metal shaping members which will be resistant to erosion when subjected to the washing action of molten metals and alloys, particularly non-ferrous metals and alloys such as copper, brass or bronze, aluminum and aluminum alloys, zinc and zinc alloys, magnesium and magnesium alloys. I

Another object of the invention is to provide a die casting dies, and other shaping members which will resist cracking or spalling when subjected to the thermal stresses created by molten metals and alloys being forced into dies and molds under pressure.

Another object of the present invention is to provide shaping members which have resistance to thermal shock.

Still another object of the invention is to provide shaping members which have resistance to erosion.

Still another object of the invention is to provide shaping members which are resistant to spalling.

Still another object of the invention is to provide shaping members which are resistant to cracking.

Still another object of the invention is to provide shaping members which have low surface roughness after continued operation.

It is another object of the present invention to provide shaping members which require cleaning less frequently.

It is another object of the invention.to provide shaping members having good mechanical properties both at room temperature and at elevated temperatures encountered in die casting operations.

Another object of the present invention is to provide shaping members which rapidly remove heat from the metals and alloys being cast.

Another object of the present invention is to provide a method of casting resulting in increased life of casting components including dies, molds, cores, core pins and other shaping members.

Another object of the present invention is to provide a method of increasing the life of casting components including dies, molds, cores, core pins and other shaping members.

Other objects will be apparent from the following description and drawings.

In the drawings:

FIG. 1 is a cross section of an exemplary die casting die or mold;

FIG. 2 is a cross section of another exemplary die or mold; and

FIG. 3 is a graph comparing the surface roughness of dies made in accordance with the present invention with various die materials of the prior art.

FIGS. 4 through 7 are perspective views of exemplary shaping members which may be utilized in accordance with the present invention.

Generally speaking, the objects of the invention are accomplished by utilizing a die, mold, core or other metal shaping member having a molding surface comprising a tungsten-ironnickel molybdenum alloy. For example, the shaping members may comprise one or more die blocks defining a portion of a die cavity, as well as cores, core pins and other metal shaping members commonly associated with non-ferrous casting, particularly die castings, fabricated from an alloy comprising about 77 weight percent tungsten by weight, the balance being essentially iron, nickel and molybdenum with said shaping member constituting at least a portion of the casting cavity. The conduit or conduits, or other means to conduct molten metal to the casting cavity may also utilize surfaces made of a tungsten-nickel-iron-molybdenum alloys, if desired.

Referring now to FIG. 1, an exemplary die casting die or mold 10 in the main comprises at least two blocks 11 and 12 each having a cavity 13 and 14 the blocks being positioned adjacent each other to form a continuous die cavity 15 for forming a metal part. As shown, the casting die is held within a block housing 16 composed of two sections 17 and 18. Molten metal from which the part is to be formed, is fed to the cavity 15, under pressure, by way of conduit 19. The shape of cavity 15 is determined by molding surfaces 13a and 14a. The shape of the cavity as shown in FIG. 1 is by way of illustration only, the particular shape being cast being dependent upon the shape of the part desired.

An important feature of the present invention lies in the material used to fabricate the shaping members such as blocks 11 and 12 which define the surfaces and 14a. The present invention makes use of a tungsten base alloy containing iron, nickel and molybdenum to give dies and other shaping members longer life even though high melting point metals and alloys such as copper, bronzes and brasses or other non-ferrous metals such as aluminum, aluminum alloys, zinc, zinc alloys, magnesium and magnesium alloys are being molded. It is within the scope of the invention to form such surfaces from a tungsten-nickel-iron-molybdenum alloy coating upon the die blocks, cores, core pins, or other shaping members.

Tungsten has little, if any, solubility in copper. This renders the material especially useful for the forming of parts from the aforementioned high melting point materials. However, pure tungsten has low mechanical properties, is relatively brittle and is difi'rcult to fabricate. Very high sintering temperatures are required, and to obtain a completely dense structure it usually must be hot worked mechanically.

On the other hand, as disclosed in Ser. No. 590,088, referenced to above, tungsten based alloys containing small percentages of iron and nickel can be formed by powder metallurgy and liquid phase sintered at reasonable temperatures to make articles having densities very near theoretical with high yield and tensile strengths, good ductility, good impact strength, and high resistance to thermal shock. Such alloys are readily machined utilizing ordinary machine shop tools and practices so that intricate cavity shapes can be readily formed. And tungsten-iron-nickel alloys are susceptible to heat treatment which increases not only their tensile proper ties, but more important for casting applications, their ductility.

It has been found that when molybdenum is added to the tungsten-iron-nickel material, some of the mechanical properties including strength of the shaping members, both at room temperature and more important at elevated temperatures is observed as well as increased resistance to thermal shock. It is believed this effect results from the strengthening of the ironnickel matrix by the solution of molybdenum in the matrix during liquid phase sintering. The amount of molybdenum added is a balance between the amount needed to be effective in increasing the mechanical properties and the amount which adversely effects the shrinkage characteristics of the material. Thus the amount of molybdenum added must be controlled such that thermal cracking due to the expansion of the com ponents of the material is avoided when the working surfaces of the die are exposed to the elevated temperature of the molten metal being cast. Yet sufficient molybdenum must be added to take advantage of the improved mechanical properties of the molybdenum containing material. Amounts of up to about 8 percent by weight have been found to suitably effect this balance; amounts less than about 0.5 percent by weight have little or no significant effect on the shaping member properties. The preferred molybdenum content is from about 2 to about 6 weight percent. Amounts of up to about 4 percent are particularly preferred.

The shaping members of the present invention should also contain from about 77 to about 98 weight percent tungsten, from 1 to about 12 percent nickel and from about 0.5 to about 7.5 percent iron. The ratio of nickel to iron in the shaping members of the present invention should be from about 1 to 1 to about 4 to l.

The preferred range for the shaping members of the present invention is from about 85 to about 95 weight percent tungsten, from about 1.5 to about 8 percent nickel, from about 0.5 to about 5 percent iron, and from about 2 to about 6 weight percent molybdenum. Preferably, the ratio of nickel to iron is from about 1.5 to 1 to about 3 to l.

The shaping members of the present invention generally have a tensile strength of at least 130,000 psi at room temperature and a yield strength of at least 85,000 psi at room temperature. Values of 140,000 psi and higher tensile and 125,000 psi and higher yield can be obtained with tungsten contents of about 90 percent. Elongation is important because the shaping members must withstand thermal shock. The elongation is usually at least 2 percent for this reason and is often at least 3 percent (inches in 2 inches). Through heat treating, elongations of from 5 to 25 percent can be achieved and elongations in this range are the most preferred for applications requiring particularly high resistance to thermal shock.

The preferred method of heat treatment comprises heating the sintered compact to a temperature of 500 1200 C. in a neutral or slightly reducing atmosphere for about one-half to 12 hours and then quenching rapidly.

Tensile strength at elevated temperature is very important for the shaping members of the present invention. It has been found that in short time tensile tests the following tensile strengths can usually be obtained with the shaping members of the present invention:

SHORT TIME TENSILE STRENGTHS Tensile Temp ("F) Strengths (psi) Preferred Typical 1,200F. 75,000 psi 100,000 psi 125,000 psi 1,500F. 52,000 psi 90,000 psi 95,000 psi |,800F. 35,000 psi 50,000 psi 54,000 psi 2,000F. 20,000 psi 30,500 psi 34,000 psi Still another important property of the shaping members of the present invention is the thermal conductivity or the rate at which heat is removed through the shaping members from the molten metals and alloys being cast. For the shaping members of the present invention, the thennal conductivity at room temperature is usually about 0.20 cgs units and preferably it is about 0.30 cgs units. The high thermal conductivity of the shaping members of the present invention tends to result in solid, sound castings; and the rapid rate of heat removal tends to reduce welding and erosion and thermal stresses.

Another important property of the shaping members of the present invention is that of the surface roughness of the shaping member cavity after prolonged use. In the case of steel shaping member surfaces, the surface roughness has been such that after as few as 6,000-10,000 cycles of casting shots the cavities must be polished and/or machined because the surface has become too rough, resulting in casting defects such as poor surface quality and/or cracking. This usually involves shutting down the operation and/or down time, etc. A surface roughness above about 300 X 10 inches or higher is often considered to be too rough.

By contrast, the shaping members of the present invention can withstand many more cycles of operation before such polishing and/or machining is necessary. The shaping surface of the shaping members of the present invention almost always have a surface roughness below about 300 X 10" inches after 50,000 cycles. It is usually below 300 X 10 inches after 100,000 cycles and very often below 300 X 10' inches after 125,000 cycles. In fact, in many instances the surface roughness is below 200 X 10 inches after 50,000 cycles, and even below 200 X 10' inches after 100,000 or 120,000 cycles.

FIGS. 4 through 7 depict various other high temperature tooling components used in the die casting and plastic injection molding industries wherein the tungsten-iron-nickelmolybdenum alloy of the present invention has been found to be remarkably superior to prior art materials used in fabricating the components. It should be understood, however, that the components shown are merely illustrative and not exhaustive in scope.

In FIG. 4 there is shown a sprue pin 40 whose working surface 41 normally forms a part of the die cavity and which is used to knock out the formed part from the die cavity. In FIG. 5 there is shown a plunger tip 50 having a working face 51. The tip is used to force molten metal into the die cavity, the molten metal being forced through the working face 51. FIG. 6 shows a core pin 60 having an outer diameter forming a working face 61 which forms the inside diameter of a casting. FIG. 7 illustrates a male 70 having a bore 71 through which the molten material for metal or plastic injection molding is fed under pressure. As such, the surface 72 forming the bore 71 is subjected to the thermal stresses imposed by the washing action of the hot material being fed through the nozzle.

With reference to FIG. 3, there is shown a graph showing the relationship of the cavities surface roughness as it varies with the number of castings made for the types of tool steels tested and the tungsteniron-nickel-molybdenum die. Note the relatively little tendency for the surface roughness of the tungsten-nickel-iron-molybdenum die to increase, even after 100,000 cycles as compared with steel at about 10,000 cycles or less.

Tests have been conducted on various tooling components such as die casting dies, core pins, plungers, sprue pins, etc. In a typical die casting die wherein brass castings were formed, 52,000 castings were made. The brass was injected into the die at a pressure of about 18,000 psi. The temperature of the brass was about 1,750 F. Under these conditions, typical tool steel dies had an average life of 5,000 castings.

EXAMPLE I With particular reference to FIG. 2, an exemplary application of the present invention is described. In FIG. 2, a die casting die or mold 20 is formed from two split sections or blocks 21 and 22, the blocks being fabricated from an alloy consisting essentially of percent tungsten, 4 percent nickel, 2 percent iron and 4 percent molybdenum by weight, the blocks being formed by liquid phase sintering. The die is held within a block housing 23 that is principally made up of two sections 24 and 25 and backing plates 36 and 37.

Each section of the die contains a cavity 28 and 29 each having a mold surface 30 and 31, the cavities being machined into the blocks. Cavities 28 and 29 together with the space 32 fonned by the spaced relationship of the blocks 21 and 22 form the continuous die cavity 33. The particular part being formed by the casting die in this instance comprises a faucet nut having approximately five-eighths inch ID. a 1 inch OD. and a length of three-fourths inch. The molten metal used to form the article is fed to the cavity through conduit 34.

After forming blocks 21 and 22 with their cavities, the blocks were heat treated to increase their ductility such that an elongation of about percent was achieved. Another die casting die identical in structure to that shown but constructed of tool steel is positioned in the split block housings similar to 24 and 25 in FIG. 2 such that comparative results could be made with the die of the present invention. Thus for every operation of the die casting machine utilizing the dies, two castings were produced, one from the tungsten-iron-nickelmolybdenum die and the other from the block housing such that various tool steels could be used.

The material used for casting was 60 percent copper-40 percent zinc alloy by weight. The temperature of the dies was maintained at about 500 F. by means of a gas heater. The temperature of the molten brass alloy was 1,750 F The alloy was injected into the die cavities at a pressure of about 18,000 ps1.

After each stroke of the die casting machine in which a casting was made, the cavities were cleaned of chips, flakes or flash remaining from the casting operation. This was done with an air blast which contained an oil, graphite, or other hydro-carbon compound. This left a carbonaceous film on the die cavities which assisted in releasing the brass casting from the dies. After eight hours, it was necessary to remove the tool steel die to clear away the hard carbon base film that had built up in the cavity. The same type of film built up or formed very slowly on the tungsten-iron-nickel-molybdenum alloy cavity and required cleaning only after 80 to 100 hours of operation. Thus there was much less down time and loss of production with the tungsten-iron-nickel-molybdenum die.

Under these conditions, the tool steel dies had an average life on the order of 5,000 castings. At this point they cracked and abraded to such an extent that the castings were not useable. The cavity surface roughness was above 300 X 10' inches. An examination of the tungsten-iron-nickel-molybdenum dies after they had produced about 36,000 castings revealed them to be essentially the same as when they had been put into operation (well below 200 X 10 inches surface roughness). In fact, the dies continued in operation until after about 130,000 cycles when the test was stopped, but at which time the surface roughness was still below 200 X 10 inches.

EXAMPLE II An aluminum base alloy containing 8.5% Si and 3.5% Cu, by weight (alloy 380) was die cast into a cup-shaped apparatus similar to that shown in FIG. 2 having an approximate CD. of 1%, ID. of b and a length of 1%. The dies were made of a tungsten base alloy consisting essentially of 4% Ni, 2% Fe and 4% Mo.

' The molten alloy was maintained at a temperature of about 1,200" F just before casting.

Flakes and chips were removed with an air blast every 80 to 100 hours as in the case in Example I.

After about 105,000 casting shots the operation was discontinued and the dies examined.

The W-Ni-Fe-Mo dies still had a surface roughness below 200 X 10 inches after approximately 105,000 cycles.

I claim:

1. A die casting shaping member having a surface, said surface having a first surface portion which defines at least a portion of the contour of at least one article to be cast; said first surface portion being made of a tungsten base material consisting essentially of about 1 to 12 weight percent nickel, about 0.5 to 7.5 weight percent iron, about 0.5 to about 8 percent molybdenum, and 77 to 98 percent by weight tungsten, the ratio of nickel to iron being from about 1:1 to about 4:1,

said tungsten material havin% a thermal conductivity of cgs units of at least about 0.20 an a short time elevated temperature strength at 1,800 F. of at least about 35,000 psi and at 1,500 F. of at least about 52,000 psi; said shaping member being resistant to erosion and wetting by molten metals being cast, as evidenced by a surface roughness of not more than about 300 X 10 inches after 50,000 casting cycles.

2. A shaping member according to claim 1 having a short time elevated temperature strength of at least about 75,000 psi at 1,200 F.

3. A shaping member according to claim 2 having a short time elevated temperature tensile strength at 2,000 F. of at least about 20,000 psi.

4. A shaping member according to claim 1 having a room temperature yield strength of at least about 85,000 psi.

5. A shaping member according to claim 4 having a room temperature elongation into inches of at least about 2 percent.

6. A shaping member according to claim 5 having a room temperature tensile strength of at least about 130,000 psi.

7. A shaping member according to claim 1 having a thermal conductivity in cgs units of at least about 0.30.

8. A shaping member according to claim 1 in which the molybdenum content is from about 2 to about 6 weight percent.

9. A shaping member according to claim 8 wherein the nickel content is from about 1.5 to about 8 percent and the iron is from about 0.5 to about 5 percent and the tungsten content is from about to 98 weight percent.

10. A shaping member according to claim 9 having a short time elevated temperature tensile strength at 1,800 F. of at least about 50,000 psi.

11. A shaping member according to claim 1 wherein said shaping member is a mold.

12. A shaping member according to claim 1 wherein said shaping member is a die.

13. A shaping member according to claim 1 wherein said shaping member is a core pin.

14. A shaping member according to claim 1 wherein said shaping member is a core.

15. A shaping member according to 9 in which the composition of said'shaping member is about percent by weight tungsten, about 4 percent by weight nickel, about 2 percent by weight iron and about 4 percent by weight molybdenum.

16. A shaping member according to claim I in which the surface roughness is not more than about 200 X 10 inches after 50,000 casting cycles.

17. A shaping member according to claim 1 in which the surface roughness is not more than about 300 X 10 inches after 100,000 casting cycles.

18. A shaping member according to claim 1 in which the surface roughness is not more than about 200 X 10 inches after 100,000 casting cycles. 

2. A shaping member according to claim 1 having a short time elevated temperature strength of at least about 75,000 psi at 1, 200* F.
 3. A shaping member according to claim 2 having a short time elevated temperature tensile strength at 2,000* F. of at least about 20,000 psi.
 4. A shaping member according to claim 1 having a room temperature yield strength of at least about 85,000 psi.
 5. A shaping member according to claim 4 having a room temperature elongation into inches of at least about 2 percent.
 6. A shaping member according to claim 5 having a room temperature tensile strength of at least about 130,000 psi.
 7. A shaping member according to claim 1 having a thermal conductivity in cgs units of at least about 0.30.
 8. A shaping member according to claim 1 in which the molybdenum content is from about 2 to about 6 weight percent.
 9. A shaping member according to claim 8 wherein the nickel content is from about 1.5 to about 8 percent and the iron is from about 0.5 to about 5 peRcent and the tungsten content is from about 90 to 98 weight percent.
 10. A shaping member according to claim 9 having a short time elevated temperature tensile strength at 1,800* F. of at least about 50,000 psi.
 11. A shaping member according to claim 1 wherein said shaping member is a mold.
 12. A shaping member according to claim 1 wherein said shaping member is a die.
 13. A shaping member according to claim 1 wherein said shaping member is a core pin.
 14. A shaping member according to claim 1 wherein said shaping member is a core.
 15. A shaping member according to 9 in which the composition of said shaping member is about 95 percent by weight tungsten, about 4 percent by weight nickel, about 2 percent by weight iron and about 4 percent by weight molybdenum.
 16. A shaping member according to claim 1 in which the surface roughness is not more than about 200 X 10 6 inches after 50,000 casting cycles.
 17. A shaping member according to claim 1 in which the surface roughness is not more than about 300 X 10 6 inches after 100, 000 casting cycles.
 18. A shaping member according to claim 1 in which the surface roughness is not more than about 200 X 10 6 inches after 100, 000 casting cycles. 